Technical Field
The present invention relates to a powder dispersant, and a powder dispersion composition and a cosmetic product containing the powder dispersant.
Background Art
Powders contained in various products such as cosmetic products and industrial materials, while exerting various functions, have high aggregation properties and therefore it is necessary to maintain uniform dispersion in such a product and stability over time, for which various dispersants have been studied. Of the cosmetic products, sunscreen cosmetics and the like having a UV protection function contain a powder as a UV absorbing scattering agent, where a micronized powder having a particle size of 10 to 500 nm is used for purposes such as increasing the UV absorption capacity of the powder and preventing the powdery finish when applied to the skin so as to improve the transparency (see Japanese Patent Laid-Open No. 08-3026, hereinafter referred to as Patent Literature (PL) 1). Further, in order to improve the UV protection function and the transparency, it is necessary to uniformly disperse the powder, for which a powder dispersant is contained therein. As a powder dispersant, ricinoleic acid and hydroxystearic acid (see Japanese Patent Laid-Open No. 06-39272, hereinafter referred to as PL2), polyhydroxystearic acid (see Japanese Patent Laid-Open No. 2012-184178, hereinafter referred to as PL3), siliconized polyglycerol (polyglycerin) (see Japanese Patent Laid-Open No. 2007-161648, hereinafter referred to as PL4), polyether modified silicone (see Japanese Patent Laid-Open No. 2001-58926, hereinafter referred to as PL5), polyglycerol modified silicone (see Japanese Patent Laid-Open No. 2004-169015, hereinafter referred to as PL6), and the like are used. The micronized powder as in PL1 is difficult to disperse because of its large surface area and a high aggregation force, and the dispersion is more difficult particularly in the case where there is a significant difference in polarity among oil agents, as in the cosmetic products. The case of using an organic UV absorber that is a compound with a high polarity and a non-polar oil agent such as silicone oil applies to the above case. In the case of using ricinoleic acid, hydroxystearic acid, or polyhydroxystearic acid as a dispersant, as in PLs2 and 3, in such oil agents, a large amount of the dispersant needs to be contained therein, where it is sticky in use, and further its stability over time is also insufficient. The silicone dispersants used in PLs4, 5, and 6 are low HLB surfactants in which a hydrophilic moiety is introduced into a silicone chain and silicone serves as a backbone, and therefore, with such dispersants, dispersion is easily maintained in a silicone oil, while a powder tends to aggregate in an organic UV absorber with a high polarity. Further, in oil-in-water (O/W) emulsified cosmetic products and water-in-oil (W/O) emulsified cosmetic products which contain water, the powder dispersibility may sometimes decrease due to the orientation of the dispersant at the interface between oil and water. Further, these dispersants have a high molecular weight, and therefore there are problems in usability such as the occurrence of stickiness.